Adding on to TDavid's suggestion, prior to doing your update you may want to do:
<BLOCKQUOTE><font size="1" face="Verdana,Arial,Helvetica">code:</font><HR><pre>
SELECT columname FROM tablename WHERE id=value
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first. That'll give you the rows that you'll be updating when you execute the UPDATE statement (so long as the DB doesn't change between the SELECT and UPDATE). If you get more than one row back, be careful. ;-)